Soil heavy metal pollution and ecological risk assessment in disturbed and undisturbed soil of Morigaon, Assam

Abstract

AbstractThe presence of heavy metals in agricultural soils has become a critical concern in the face of increased environmental scrutiny, highlighting the relationship between human and natural impacts on our land. This study focused on examining heavy metal contamination levels including Copper (Cu), Chromium (Cr), Cobalt (Co), Lead (Pb), Iron (Fe), Zinc (Zn), Nickel (Ni) and Manganese (Mn) conducting an ecological risk assessment in the Morigaon district's paddy fields, which are characterized by disturbed soils. Undisturbed playground soils of the Morigaon district were taken as control. Based on the averages of all locations and the corresponding contamination factor (Cf) for paddy field, it was found that the soil's Cr (0.56 to 0.84), Fe (0.11 to 0.13), Mn (0.38 to 0.78), and Zn (0.35 to 0.65) contamination is low, with Cf < 1 for all seasons. Observed levels of Cu, Ni, and Pb showed moderate contamination throughout seasons, with contamination factors (Cf) ranging from 1 to 3. Meanwhile, Co exhibited a greater amount of contamination in the disturbed soil, with Cf ranging from 3 to 6, indicating significant contamination. Higher degree of contamination (CD) of the sampling sites (10.71 to 14.72) might have been due to metal contamination, especially Co, Ni and Pb. Undisturbed soil showed a comparatively lesser degree of contamination because of an absence of physical or chemical disturbances. In particular, Ni contents of disturbed and undisturbed sites were excessively higher than the worldwide average. Significant variations from global averages were particularly noted for Co and Pb. Conversely, Cr, Mn, and Zn demonstrated minimal variations when compared to these averages. Additionally, metrics such as Enrichment Factors (EF), Potential Ecological Risk Index (PERI) and Ecological Risk Index (Er) were elevated in the disturbed soils relative to their undisturbed counterparts. The findings indicated that anthropogenic activities have significantly negatively influenced the Morigaon district paddy field's soil quality and agriculture.